The present invention relates to an oil feed system for a variable-crown roll, which roll comprises a stationary roll axle and a roll mantle that is revolvingly arranged on the stationary roll axle and that is supported on the roll axle by means of hydraulic loading elements acting upon the inner face of the roll mantle in the radial direction. By means of the loading elements, the axial profile of the roll mantle is regulated. An axial through hole has been formed in the roll axle and communicates with cylinder bores or equivalent of the hydraulic loading elements through substantially radial bores or equivalent ducts. In the axial through hole, at least oil feed pipes are installed, at least through one of the roll ends, through which a pressure fluid is fed to the hydraulic loading elements.
In the prior art, a number of different variable-crown rolls for paper machines or paper finishing machines are known, for which rolls different designations are used, such as variable-crown roll, roll adjustable in zones. Generally, these rolls comprise a massive or tubular, stationary roll axle and a roll mantle that is arranged to revolve around the axle. Between the axle and the mantle, glide-shoe arrangements that act upon the inner face of the mantle and/or a chamber or series of chambers for pressure fluid are arranged such that the axial profile of the mantle at the nip can be aligned or adjusted in a desired manner, e.g., to a desired profile.
In variable-crown rolls, a complex oil distribution system is needed because the roll has a number of points to which oil must be passed. These points include the zones in a variable-crown roll, to which pressure fluid must be passed, various points that require lubrication, to which a lubricant is passed, possible roll heating means for the supply of heating fluid, and equivalent objects that consume oil. Since a roll has a number of various oil-consuming objects, the roll must, of course, also include a system of ducts for the exhaust oil. In the prior art, the system of oil distribution ducts has been accomplished in a variable-crown roll in a number of different alternative ways.
One prior art construction is described, e.g., in U.S. Pat. No. 4,222,324, in which a separate axial bore is formed into the roll axle of the variable-crown roll for each zone in the variable-crown roll, through which bores the oil is passed into the zones through radial bores. Thus, in such a roll, it is necessary to make a considerable amount of bores and various pipe systems. This results in the drawback that the cost of manufacture of the system of oil distribution ducts is quite high, and the system of ducts requires very careful manufacture, for various rubbish, dirt, machining chips and equivalent readily remain in the ducts. Moreover, for possible heating and lubrication of the roll, it has been necessary to form the required bores into the roll axle, or it has been necessary to provide the roll with a specific separate system of ducts for these functions.
A second prior art construction is described, e.g., in U.S. Pat. No. 4,292,716, wherein the roll has an axial bore having a large diameter formed into the roll axle, in which bore a series of pipes is arranged. Through the pipes, the pressure fluid is passed to the hydrostatic loading elements placed in the zones of the roll. The series of pipes is connected with a number of sealing elements by whose means the series of pipes is sealed in relation to the axial bore of the roll between the zones. It is a significant drawback of this arrangement that the series of pipes comprises a number of sealing points and, thus, it comprises a number of seals which are susceptible to leakage. Moreover, the pipes included in the series of pipes must be of very high quality to withstand the pressures required by the zones. A further problem in this construction is involved in the seal friction. It also results from these drawbacks that, for example, the construction is very expensive and complicated to manufacture. Also, in such a construction, separate systems of ducts are required, for example, for possible heating of the roll and for the points to be lubricated. Furthermore, if the zones in the roll were to be made more frequent, these problems would be emphasized further, as the number of objects to be sealed would increase accordingly.
A further prior art construction is described, e.g., in U.S. Pat. No. 4,106,405. In the construction disclosed in this patent, a central hole having a large diameter is formed into the roll axle. Coaxially arranged pipes are arranged in the hole and through which the pressure fluid is fed into the zones of the roll. This construction also involves a number of different drawbacks, of which it should be mentioned, for example, that the wall thicknesses of the pipes must be large, because the pressures required by adjacent zones may differ from one another quite substantially. Thus, the risk of buckling of the pipes is quite high. Also, the sealing of the pipes is quite problematic in this construction, for the pipes must be sealed in relation to one another, on one hand, and they must be sealed in relation to the central hole formed into the roll axle, on the other hand. From the point of view of the manufacture of this roll, such an oil distribution system is complicated and expensive. Also in this system, for possible heating of the roll, the roll must be provided with a separate fluid distribution system.
Another prior art construction is described in U.S. Pat. No. 5,103,542. In the construction disclosed in this patent, a system of oil distribution ducts in the roll is composed of one profile, which is arranged in an axial hole formed into the roll axle. It is an advantage of this profile construction that, if necessary, the profile may include ducts for the pressure fluid passing into the zones, lubricant ducts, an exhaust oil duct, and in addition, a system of ducts for heating fluid. Indeed, such a construction is quite advantageous when the distribution of zones in the roll is not so dense, i.e., when the number of zones in the roll is not high. However, on the other hand, in a case in which the number of zones must be increased, this construction involves the drawbacks that are related to the fact that the number of points to be sealed becomes higher. Thus, when the profile construction is employed, the number of ducts is quite limited. Owing to the large number of seals and the small plays, the installation of the profile into the roll axle is quite difficult, especially when the number of zones is high. In order that an adequate sealing quality of the seals of the profile could be secured, it has been necessary to hone the central hole in the axle.